We continue our networking series, utilising analogies to explain:

What is multi-plexing?

Abstract definition: it’s when you have multiple signals combined into one signal, and then shared over a medium.

An Example of Failed Multi-plexing?

Imagine you are in a crowded room - with hundreds of people talking over each other. How can you understand what anyone else is saying? It is too difficult and confusing to listen to so many sounds at the same time.

In this case multiple sound waves (i.e. signals) are emitted through a sigle medium (i.e. the airwaves). But it is very difficult for someone listening to separate all the people speaking, and interpret them as a message.

Rules are needed

Protocols are needed to avoid chaos:

(1) Time Division Multi-plexing

• Freddie speaks for 30 seconds, then
• Brians for another 30, then
• Roger, then
• Deacon

All for take turns to speak. They will be the only voice speaking at one time. The listener is made to realise that everyone is taking turns. This is an example of Time division multi-plexing.

(2) Frequency Division Multiplexing

In human interaction, when two people talk at the same time, we implicitly recognise their voices. This analogy does not apply well in network communications. However, we can communicate using different frequencies. To use the Queen example, we can request all the band members to speak at the same time, however, they must sing using different pitches:

• Freddie: uses high falsetto, (Example)
• Roger: soprano;
• Brian: tenor
• Deacon can stick to the bass.

The listener can immediately recognise all the speakers, if he focuses on the different pitches (i.e. frequencies), and he can immediately understand who is speaking (or singing) because they are all using different pitches, even though they are all singing at the same time.

Other Forms of Multiplexing

Here is another form of multi-plexing: multiple letters are written on the same piece of paper - except they are written across each other. It is suprisingly easy to read and undestand:

However, if they were written on the same line, over each other - then it would probably be much harder to interpret.

Hopefully you understand multiplexing as a concept, and the need for protocols to communicate with multiplexing.